The production method for flu vaccines, in other words, renders certain influenza viral strains nearly useless. This is obviously part of the reason why people who get flu shots still manage to catch the flu with alarming frequency. (That failure of flu vaccine effectiveness, ironically, is used by the media to encourage people to get even more flu shots, as if receiving multiple injections of a quack vaccine might magically make it work better.)

From the abstract of the study:

The effectiveness of the annual influenza vaccine has declined in recent years, especially for the H3N2 component, and is a concern for global public health. A major cause for this lack in effectiveness has been attributed to the egg-based vaccine production process… Overall, these findings help explain the low effectiveness of the seasonal vaccine against H3N2 viruses… It is common to use chicken eggs for culturing clinical isolates and for large-scale production of vaccines. However, influenza virus often mutates to adapt to being grown in chicken eggs, which can influence antigenicity and hence vaccine effectiveness.

In the summary of the paper, the author openly admits that flu vaccines don't work and urges the vaccine industry to urgently change its production practices:

Our study describes a mechanism for the low influenza vaccine effectiveness and reaffirms the urgency for replacing the egg-based production of influenza vaccines…

The author even admits that flu vaccine propaganda is largely false, describing how the goal of flu shot immunization has still not been achieved even after 70 years of quackery, propaganda and social engineering to push vaccines that simply don't work:

Despite the first commercial influenza vaccines being approved in the US more than 70 years ago, complete and broad protection from an influenza vaccine has remained out of reach. Furthermore, in the past decade, the effectiveness of the seasonal vaccine against H3N2 viruses has been particularly low.